In two-dimensional resistive film systems on an insulative substrate, it is common practice to regard the film thickness as relatively invariant and to express the sheet resistivity of the film in terms of ohms per unit area, in conjunction with a geometric factor as the number of unit areas (squares) in series. Higher resistance values can be achieved in such film systems by either using a material or composition of higher sheet resistivity or by increasing the number of serial squares, or both. In well-known thin film resistor systems of the foil type or the vapor-deposited type the resistance value is changed by changing the geometry, i.e., by adjusting the number of squares. In thick film resistors the sheet resistivity is adjusted over a range of several decades by changing the composition of the starting material used for depositing the resistive film. Each of these approaches presents difficulties when attempting to fabricate film resistors or film resistor networks of high resistance value. In thin film resistor technology, the number of squares in series can be increased by decreasing the size or area of the resistive squares or, alternatively, the area of the substrate can be increased if a desired high resistance value is to be achieved. However, both of these approaches have practical limits. In thick film resistor technology, a high resistance value is, in principle, achievable by increasing the resistivity of the thick film material, generally a composite material of conductive particles in an insulative matrix. Thus, in principle, high resistance value thick film resistors or networks can be prepared by reducing the concentration of the conductive particles in the insulative matrix of the thick film composition. In practice, however, it has been found that thick film resistors prepared from very high sheet resistivity compositions show degraded performance or degraded operating characteristics, particularly regarding long-term stability, voltage coefficient of resistance, and current noise index.
Thus, it would be desirable to fabricate high resistance value film resistors and film resistor networks which have stable and reproducible operating characteristics.